Casandra is training for a 10 mile race. On the first day of running training she runs 4 miles, each day after that she adds on 0.5 mile. On what day will Casandra run 8 miles?

Let the number of days needed be x.

First day = 4 miles = 3.5 + 0.5

Second day = 3.5 + 0.5 (2)

Third day = 3.5 + 0.5 (3)

Equation: 3.5 + 0.5x

Find the number of days needed to run 8 miles:

3.5 + 0.5x = 8

0.5x = 4.5

x = 9

Answer: Casandra 8 miles on the 9th day.